=over

=item $EFFECTIVE_USER_ID

=item $EUID

=item $>
X<< $> >> X<$EUID> X<$EFFECTIVE_USER_ID>

The effective uid of this process.  For example:

    $< = $>;            # set real to effective uid
    ($<,$>) = ($>,$<);  # swap real and effective uids

You can change both the effective uid and the real uid at the same
time by using C<POSIX::setuid()>.  Changes to C<< $> >> require a check
to C<$!> to detect any possible errors after an attempted change.

C<< $< >> and C<< $> >> can be swapped only on machines
supporting C<setreuid()>.

Mnemonic: it's the uid you went I<to>, if you're running setuid.

=back